For the VimGolf challenge “List the first 100 prime numbers”, there’s a solution that uses a regular expression to detect prime numbers. At 43 keystokes, it’s not the winning solution, but I think it’s the most interesting one. It uses a few clever Vim tricks, including macros, control-a to increment, the very magic pattern switch, and the :global command. There’s a lot to learn from those 43 keystrokes, so let’s study it!